JP2002327202A - Magnetic particulate powder of composite metal mainly including iron, manufacturing method therefor, and magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide magnetic particulate powder of composite metal mainly containing iron, superior in dispersibility and oxidation stability, while maintaining adequate magnetic properties. SOLUTION: The magnetic particulate powder of composite metal mainly containing iron is characterized in that magnetic metal particulate powder mainly containing iron has a mean major axis diameter of 0.02-0.30 μm and sodium content of 10 ppm or less, and that polyether modified polysiloxane of 0.02-10 wt.% in terms of Si adheres to the surface of each magnetic particle powder. The manufacturing method comprises dispersing the metal particulate powder of composite metal mainly containing iron into an aqueous solution, washing it in the suspended state in water, then adding polyether modified polysiloxane of 0.02-10 pts.wt. in terms of Si based on the quantity of the metallic magnetic particles, to the aqueous suspension containing the metallic magnetic particles mainly containing iron, stirring, dehydrating, and filtrating it.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention provides a composite metal magnetic particle powder containing iron as a main component which has excellent dispersibility and excellent oxidation stability while maintaining good magnetic properties. is there.

[0002]

2. Description of the Related Art In recent years, devices for magnetic recording / reproducing for audio, video, and computers have been significantly reduced in size and weight, long-time recording, high-density recording, or an increase in storage capacity. Demands for higher performance and higher density recording of magnetic tapes and magnetic disks as magnetic recording media are increasing more and more.

[0003] That is, there is a demand for a magnetic recording medium to have high image quality, high image quality, high output characteristics, especially improved frequency characteristics, and improved storage stability and durability.

[0004] These characteristics of the magnetic recording medium are closely related to the magnetic particle powder used in the magnetic recording medium, and in recent years, the coercive force is higher than that of the conventional iron oxide magnetic particle powder. Magnetic metal particles containing iron as a main component having a large saturation magnetization value have attracted attention, digital audio tape (DAT), 8 mm video tape, Hi-8
It is used for tapes, W-VHS tapes for high vision, DVC tapes of digital recording system, etc., and for computers, removable disks such as Zips and super disks and Hi-FDs.

However, iron-based metal magnetic particles used for magnetic recording media are very fine particles of 1 μm or less, especially about 0.02 to 0.20 μm. This is disadvantageous in that the magnetic properties are deteriorated, and in particular, the coercive force value and the saturation magnetization value are reduced.

This fact is described in Japanese Unexamined Patent Publication No. Hei 5-81648. "... The ferromagnetic metal fine particles have a high surface activity and are easily oxidized in the atmosphere, and may be accompanied by ignition. Such a property tends to become stronger as the magnetic powder becomes finer with the reduction in noise of the magnetic recording medium. When used as a magnetic powder, during storage of the ferromagnetic metal fine particles, or during the process of coating with a resin or an organic solvent, etc., and further after application on a support such as a polyester film to form a sheet. During storage under conditions such as a predetermined atmosphere, temperature, humidity, etc., oxidation mainly due to the influence of oxygen, a certain gas, moisture, etc. progresses, and magnetic properties such as saturation magnetization deteriorate over time. Thalassa is, it is as described there was a problem with the storage stability. ... "become.

Accordingly, in order to maintain the characteristics of a magnetic recording medium using iron-based metal magnetic particle powder as the magnetic particle powder for a long period of time, the iron-based metal magnetic particle powder must be oxidized. Excellent stability is strongly required.

[0008] Further, as one of the causes for lowering the magnetic properties, storage stability and dispersion stability of the coating material of the magnetic recording medium, the content of soluble alkali metal, especially soluble sodium, contained in the magnetic recording medium is considered. It is pointed out that the amount is large.

Hereinafter, this fact will be described in detail.

That is, generally, the magnetic metal particles containing iron as a main component are iron-containing precipitates obtained by reacting an aqueous ferrous salt solution with an aqueous alkali solution such as sodium hydroxide, potassium hydroxide, and sodium carbonate. Goethite particles obtained by performing an oxidation reaction by passing an oxygen-containing gas such as air through a suspension containing air, hematite particles obtained by heating and dehydrating the goethite particles, or, in addition to iron, It is obtained by using a particle powder containing a different element as a starting material and heating and reducing the starting material in a reducing gas atmosphere.

Due to the above-mentioned production method, metal magnetic particle powder containing iron as a main component contains sodium and calcium which is unavoidably mixed in the production method, and contains a soluble sodium salt and a soluble calcium salt. In this case, there is a problem because a compound derived from a soluble salt such as a soluble sodium salt or a soluble calcium salt contained when used in a magnetic recording medium is deposited on a magnetic coating film and a magnetic head. This fact is described in Japanese Unexamined Patent Publication No. Hei 9-305958, "When the total amount of the water-soluble ions contained in the magnetic material, the non-magnetic material, the carbon black and the filler used in each layer exceeds a certain amount, under high temperature and high humidity conditions When running after storage, the coefficient of friction increased, and in extreme cases, the phenomenon of sticking occurred and the running was stopped, and in extreme cases, the precipitates resulted in spacing loss and the reproduction output of the magnetic tape was reduced. Further, the metal head is corroded and the recording / reproducing characteristics are deteriorated. "

The method of reducing the soluble salt in the metal magnetic particle powder containing iron as a main component is as follows: 1) Do not use an alkaline aqueous solution containing an alkali metal such as sodium hydroxide as a starting material; 2) Wash the soluble salt with water Either of these methods has been adopted.
The present invention relates to the method 2).

In the case of washing with water, there are a case where each product in the process of manufacturing metal magnetic particle powder containing iron as a main component is washed with water and a case where the obtained metal magnetic particle powder containing iron as a main component is washed with water. It is conceivable that, in the method for producing the metal magnetic particle powder containing iron as a main component, when washing is performed at the stage of the goethite particle powder and the hematite particle powder, which are the starting materials, what is removed is the particle powder. Since it is only a water-soluble salt of, when reduced to iron-based metal magnetic particle powder, insoluble impurities contained in the particles move to the particle surface and precipitate as a soluble salt. come. This fact is described in Japanese Unexamined Patent Publication No. 7-22224, "In order to reduce the content of Group 1a elements in the periodic table to 0.05% by weight or less, if these elements are inevitably mixed in the production process, they must be removed. It is evident from the description that iron oxide oxyhydroxide, iron oxide, and metal magnetic powder are segregated on the particle surface as the process proceeds. "

When the metal magnetic particles containing iron as the main component are washed with water, the magnetic characteristics such as the coercive force of the metal magnetic particles containing iron as the main component are reduced, so that the high magnetic characteristics are maintained. Is difficult to do. Furthermore, since the surface tension of water is high, the metal magnetic particle powder containing iron as a main component after washing becomes a hard agglomerate, has poor dispersibility at the time of preparing a magnetic paint, and when a magnetic coating film is used, iron is the main component. Cannot exhibit the high magnetic properties originally possessed by the metallic magnetic particles.

Incidentally, techniques for reducing impurities such as soluble sodium are disclosed in JP-A-56-51029, JP-A-7-22224, JP-A-8-172005, JP-A-9-231546 and JP-A-9-231546. 9-305
958, JP-A-10-69629 and the like. On the other hand, in order to improve the oxidation stability and dispersibility of metal magnetic particle powder containing iron as a main component, a technique of performing a surface treatment with polysiloxane is disclosed in JP-A-52-155398, JP-A-59-23801, JP-A-63-52
No. 327, etc.

[0016]

It is currently the most difficult to produce iron-based metal magnetic particles having excellent dispersibility and excellent oxidation stability while maintaining good magnetic properties. Although required, metal magnetic particles containing iron as a main component that sufficiently satisfy the above-mentioned properties have not been provided yet.

That is, JP-A-56-51029 discloses that the ferromagnetic metal particles are washed with an aqueous solvent (water or a mixture of water and an organic solvent containing 50% or more of water). However, when washed with water, the resulting ferromagnetic metal particle powder becomes hard agglomerates, and when washed with a mixture of water and an organic solvent, the soluble metal salt becomes an organic solvent. Is not soluble, and it is difficult to say that the soluble sodium salt can be sufficiently reduced. In addition, although surface treatment with a surfactant is described after washing with water, it is intended to improve the wetting with a binder, and cannot be said to be a magnetic particle powder having excellent oxidation stability.

Also, the above-mentioned Japanese Patent Application Laid-Open No. 7-22224,
JP-A-8-172005, JP-A-9-23154
No. 6, JP-A-9-305958, JP-A-9-305
Japanese Patent Application Laid-Open No. 69629/1992 describes washing with water as metal magnetic particle powder containing iron as a main component. However, when washing with water, the obtained metal magnetic particle powder containing iron as a main component is: It becomes a hard aggregate.

The above-mentioned JP-A-52-155398, JP-A-59-23801 and JP-A-63-5
No. 2327 describes that the surface of the magnetic particle powder is coated with a silicon compound. However, since the soluble sodium salt is not sufficiently removed by washing with water, it cannot be said that the oxidation stability is sufficient.

Therefore, the present invention mainly provides iron which has excellent dispersibility and excellent oxidation stability due to the reduction of soluble salts as much as possible while maintaining good magnetic properties. It is a technical object to obtain metal magnetic particles as components.

[0021]

The above technical objects can be achieved by the present invention as described below.

That is, according to the present invention, the average major axis diameter is 0.02 to 0.02.
0.30 μm and a polyether-modified polysiloxane having a sodium content of 10 ppm or less on each particle surface of iron-based metal magnetic particle powder having a sodium content of 0.02 to It is a composite metal magnetic particle powder containing iron as a main component, which is characterized by being attached by 10% by weight (Invention 1).

In the present invention, the metal magnetic particles mainly composed of iron are dispersed in an aqueous solution, washed with an aqueous suspension, and then washed with water. After adding 0.02 to 10 parts by weight of a polyether-modified polysiloxane in terms of Si with respect to the amount of metal magnetic particles containing iron as a main component in the aqueous suspension and stirring, the mixture is dehydrated. The present invention provides a method for producing a composite metal magnetic particle powder containing iron as a main component according to the first aspect of the present invention, which is characterized by filtration (Invention 2).

The present invention also relates to a magnetic recording medium comprising a non-magnetic support, a magnetic recording layer containing a magnetic particle powder formed on the non-magnetic support and a binder resin, wherein the magnetic particle powder is a magnetic recording medium. A magnetic recording medium characterized in that it is a composite metal magnetic particle powder containing iron as a main component (Invention 3).

The present invention also provides a non-magnetic support, a non-magnetic underlayer containing non-magnetic particle powder and a binder resin formed on the non-magnetic support, and a non-magnetic under layer formed on the non-magnetic under layer. A magnetic recording medium comprising a magnetic recording layer containing particle powder and a binder resin, wherein the magnetic particle powder is a composite metal magnetic particle powder containing iron as a main component according to the first aspect of the present invention. (The present invention 4).

Next, the configuration of the present invention will be described in more detail.

First, the composite metal magnetic particles containing iron as a main component according to the present invention will be described.

The adhesion amount of the polyether-modified polysiloxane in the composite metal magnetic particles containing iron as the main component according to the present invention is 0.02% by weight in terms of Si with respect to the metal magnetic particles containing iron as the main component. If it is less than 10, it is difficult to obtain composite metal magnetic particles having iron as a main component and having excellent oxidation stability. If it exceeds 10% by weight, the oxidation stability effect is saturated and there is no point in adding more than necessary. Further, an increase in the non-magnetic component is not preferable because the magnetic properties of the obtained composite metal magnetic particle powder containing iron as a main component are deteriorated. Preferably, the content is 0.04 to 5% by weight in terms of Si with respect to the metal magnetic particle powder containing iron as a main component.

When the average major axis diameter of the composite metal magnetic particles containing iron as the main component according to the present invention exceeds 0.30 μm, the composite metal magnetic particles containing iron as the main component become large particles. When the magnetic recording layer is formed by using, the surface smoothness of the coating film tends to be impaired. Average major axis diameter is 0.0
When the particle size is less than 2 μm, aggregation tends to occur due to an increase in intermolecular force due to finer particles, so that dispersibility in a vehicle at the time of manufacturing a magnetic coating material is reduced. In consideration of the surface smoothness of the coating film and the dispersibility in a vehicle during the production of the magnetic paint, the average major axis diameter is preferably from 0.03 to 0.25 μm.

The content of the soluble sodium salt in the composite metal magnetic particles containing iron as a main component according to the present invention is 10 ppm.
It is as follows. Soluble sodium salt content is 10ppm
When the ratio exceeds 1, the oxidation stability and dispersibility of the composite metal magnetic particles containing iron as a main component decrease, and the storage stability of the magnetic recording medium decreases. Preferably it is 8 ppm or less.

The particle shape of the composite metal magnetic particles containing iron as a main component according to the present invention is acicular. Here, “needle”
Needless to say, the shape includes a spindle shape, a rice grain shape, and the like, as well as a literal needle shape.

The average short axis diameter of the composite metal magnetic particles containing iron as a main component according to the present invention is preferably 0.001 to 0.15 μm, more preferably 0.0015 to 0.125 μm.
m. When the average minor axis diameter is less than 0.001 μm, aggregation tends to occur due to an increase in intermolecular force due to finer particles, so that dispersibility in a vehicle at the time of producing a magnetic paint is reduced. Those having an average minor axis diameter of 0.15 μm or more are difficult to obtain industrially.

The axial ratio of the composite metal magnetic particles containing iron as a main component according to the present invention is preferably 2 or more, more preferably 3 or more, and the upper limit thereof is 20, preferably 15. When the axial ratio exceeds 20, the entanglement of the particles increases, and the dispersibility in the vehicle during the production of the magnetic paint decreases. When the axial ratio is less than 2, the coating strength of the obtained magnetic recording medium decreases.

The composite metal magnetic particles mainly composed of iron according to the present invention preferably have a geometric standard deviation of 2.5 or less,
More preferably, it is 2.3 or less. If the geometric standard deviation value exceeds 2.5, the uniform dispersion is hindered by the existing coarse particles, so that the dispersibility in the vehicle during the production of the magnetic paint decreases. The lower limit of the geometric standard deviation value is 1.01, and a value less than 1.01 is difficult to obtain industrially.

The BET specific surface area of the composite metal magnetic particles containing iron as a main component according to the present invention has a BET specific surface area of 35 to 100 m ² / g.
Is more preferable, more preferably 38 to 90 m < ² > / g, and most preferably 40 to 80 m < ² > / g. When the BET specific surface area value is less than 35 m ² / g, the composite metal magnetic particle powder containing iron as a main component is coarse or particles that have been sintered between particles. When the magnetic recording layer is formed by this, the surface smoothness of the coating film tends to be impaired. When the BET specific surface area exceeds 100 m ² / g, aggregation tends to occur due to an increase in intermolecular force due to finer particles, so that dispersibility in a vehicle at the time of manufacturing a magnetic coating material is reduced.

The change rate of the coercive force value indicating the oxidation stability of the composite metal magnetic particles containing iron as a main component according to the present invention is 12
% Or less, more preferably 10% or less,
The rate of change of the saturation magnetization is preferably 12% or less, more preferably 10% or less.

The ease of unraveling of the composite metal magnetic particles containing iron as a main component according to the present invention is determined by the evaluation method 5 or 4 described later.
And more preferably 5.

The composite metal magnetic particles containing iron as a main component according to the present invention contain 0.5 to 50 atomic% of cobalt in terms of Co, 0.5 to 30 atomic% of aluminum in terms of Al, It is preferable to contain a rare earth element in an amount of 0.5 to 30 atomic% in terms of the rare earth element.

The magnetic characteristics of the composite metal magnetic particles containing iron as a main component according to the present invention have a coercive force value of 63.7 to 278.
5 kA / m (800-3500 Oe) is preferred, and more preferably 71.6-278.5 kA / m (900-3).
500 Oe) and a saturation magnetization value of 90 to 170 Am ² /
kg (90-170 emu / g), more preferably 100-170 Am ² / kg (100-170 emu).
mu / g).

Next, a method for producing the composite metal magnetic particles containing iron as a main component according to the present invention will be described.

The metal magnetic particle powder containing iron as a main component used in the present invention may be any of those usually used for magnetic recording media. For example, ferrous salt aqueous solution, sodium hydroxide, potassium hydroxide, carbonate A goethite particle powder obtained by performing an oxidation reaction by passing an oxygen-containing gas such as air through a suspension containing an iron-containing precipitate obtained by reacting with an aqueous alkali solution such as sodium, and heating and dehydrating the goethite particle powder. Hematite particle powder obtained as described above, or a particle powder containing a different element other than iron in the particle powder as a starting material, and the starting material is 350 to
After heat-reduction in a temperature range of 700 ° C., a metal magnetic particle powder mainly composed of iron whose surface is oxidized may be used.

The surface oxidation treatment is performed in an atmosphere of an inert gas containing oxygen. As the inert gas atmosphere, nitrogen gas, helium gas, argon gas and the like are preferable, and nitrogen gas is particularly preferable. The oxygen content is preferably 0.1 to 5 vol%, and it is preferable to gradually increase the oxygen content to a predetermined amount. Further, the inert gas atmosphere may contain water vapor. When water vapor is contained, metal magnetic particle powder containing iron as a main component and having a high coercive force value is easily obtained.

The surface oxidation temperature is 40 to 200 ° C.
And more preferably 40 to 180 ° C. 4
If the temperature is lower than 0 ° C., it is difficult to form a surface oxide layer having a sufficient thickness, and the magnetic properties are significantly reduced by washing with water. When the temperature is higher than 200 ° C., the shape of the particles is changed, particularly, a large amount of oxide is generated, so that the short axis is extremely expanded, and in some cases, the shape is easily broken, which is not preferable.

The magnetic metal particles containing iron as a main component are roughly pulverized and washed with water.

In the water washing according to the second aspect of the invention, metal magnetic particles containing iron as a main component are put into water, dispersed, and washed in a water suspension state. Rinsing measures the electrical conductivity of the filtrate and
It is preferable to wash with water until it becomes 0 μS / cm or less.

The water used for washing is ion-exchanged water. The higher the water temperature, the more the soluble salts can be reduced.

Next, a predetermined amount of a polyether-modified polysiloxane is added to the water suspension containing the metal magnetic particles containing iron as a main component after the water washing, followed by stirring.

Before the addition of the polyether-modified polysiloxane, the concentration of the aqueous suspension is previously adjusted to 1 to 500 g / l.
It is preferable to adjust it.

As the polyether-modified polysiloxane in the present invention 2, one or more kinds selected from the polyether-modified polysiloxane shown in Chemical formula 1 can be used.

The molecular weight of the polyether-modified polysiloxane is preferably in the range of 350 to 500,000, more preferably in the range of 1000 to 100,000, and most preferably in the range of 2000 to 50,000.

[0051]

Embedded image

The amount of the polyether-modified polysiloxane added is 0.02 to 10% by weight in terms of Si with respect to the amount of metal magnetic particles containing iron as a main component in the aqueous suspension. 0.
If it is less than 02% by weight, the dispersibility and the oxidative stability decrease. If the content exceeds 10% by weight, the effect is saturated, and there is no point in adding more than necessary. Preferably 0.04 to
5 parts by weight.

When the amount is less than 0.02% by weight, the surface tension of the slurry cannot be sufficiently reduced, so that it is difficult to sufficiently reduce the soluble salt, and the obtained iron is the main component. Cannot improve the ease of loosening of the composite metal magnetic particles.

After adding and stirring the polyether-modified polysiloxane, dehydration, filtration and drying are carried out in a conventional manner.

The composite metal magnetic particles containing iron as a main component obtained by the method of the present invention maintain good magnetic properties even after the water washing treatment, and the rate of change of the coercive force before and after the water washing treatment is as follows. It is preferably at most 5%, more preferably 4.
It is 5% or less, and the rate of change of the saturation magnetization is preferably 5% or less, more preferably 4.5% or less.

Next, the magnetic recording medium according to the present invention will be described.

Examples of the non-magnetic support in the present invention include synthetic resin films such as polyethylene terephthalate, polyethylene, polypropylene, polycarbonate, polyethylene naphthalate, polyamide, polyamide imide, and polyimide commonly used for magnetic recording media, aluminum, stainless steel, and the like. Metal foils and plates and various types of paper can be used, and the thickness varies depending on the material, but is usually 1.0 to 300 μm, preferably 2.0 to 20 μm.
0 μm.

In the case of a magnetic disk, polyethylene terephthalate is usually used, and its thickness is usually 50 to 30.
0 μm, preferably 60 to 200 μm. In the case of a magnetic tape, when polyethylene terephthalate is used, its thickness is usually 3 to 100 μm, preferably 4 to 100 μm.
When polyethylene naphthalate is used, its thickness is usually 3 to 50 μm, preferably 4 to 50 μm.
When a polyamide is used, its thickness is usually 2 to 10 µm, preferably 3 to 7 µm.

As binder resins, vinyl chloride-vinyl acetate copolymers, urethane resins, vinyl chloride-vinyl acetate-maleic acid copolymers, urethane elastomers, butadiene-acrylonitrile copolymers commonly used in the production of magnetic recording media are used. Polymers, polyvinyl butyral, cellulose derivatives such as nitrocellulose, polyester resins,
Synthetic rubber resins such as polybutadiene, epoxy resins, polyamide resins, polyisocyanates, electron beam-curable acrylic urethane resins and the like and mixtures thereof can be used.

Further, each of the binder resins has -OH, -C
OOH, -SO₃M, -OPO₂M ₂, -NH₂Etc pole
(Where M is H, Na, K)
You may. Iron-based composites in the production of magnetic paints
Consider the dispersibility of the composite metal magnetic particles in the vehicle
If the polar groups are -COOH, -SO₃Contains M
Binder resins are preferred.

The coating thickness of the magnetic recording layer formed on the nonmagnetic support is preferably in the range of 0.01 to 5.0 μm.
When the thickness is less than 0.01 μm, uniform coating is difficult and uneven coating easily occurs. When the thickness exceeds 5.0 μm, it is difficult to obtain desired electromagnetic conversion characteristics due to the influence of a demagnetizing field. More preferably, it is in the range of 0.05 to 4.0 μm.

The mixing ratio of the composite metal magnetic particle powder containing iron as a main component and the binder resin in the magnetic recording layer is such that the composite metal magnetic particle powder containing iron as a main component is added to 100 parts by weight of the binder resin. The amount is preferably 5 to 2000 parts by weight, more preferably 100 to 1000 parts by weight.

When the amount of the composite metal magnetic particles containing iron as the main component is less than 5 parts by weight, the amount of the composite metal magnetic particles containing iron as the main component in the magnetic paint is too small, so that when the coating film is formed, In addition, a layer in which the composite metal magnetic particles containing iron as the main component is continuously dispersed cannot be obtained, and the smoothness of the coating film surface and the coating film strength become insufficient. If it exceeds 2000 parts by weight,
Since the amount of the composite metal magnetic particles containing iron as the main component is too large relative to the amount of the binder resin, the composite metal magnetic particles containing iron as the main component are not sufficiently dispersed in the magnetic paint. When formed into a film, it is difficult to obtain a coating film having a sufficiently smooth surface. Further, since the composite metal magnetic particles containing iron as a main component are not sufficiently bound by the binder resin, the obtained coating film tends to be brittle.

In the magnetic recording layer, known lubricants, abrasives, antistatic agents and the like used for the magnetic recording medium are required, and if necessary, about 0.1 to 50 parts by weight with respect to 100 parts by weight of the binder resin. May be included.

The magnetic recording medium according to the present invention 3 has a coercive force value of 63.7 to 278.5 kA / m (800 to 3500O
e) is preferred, more preferably 71.6 to 278.5.
kA / m (900 to 3500 Oe), squareness ratio (residual magnetic flux density Br / saturated magnetic flux density Bm) of 0.85 to 0.95, preferably 0.86 to 0.95, and the glossiness of the coating film It is preferably 195 to 300%, more preferably 200 to 300%, and the surface roughness Ra 8.5 of the coating film.
nm or less, more preferably 2.0 to 8.0 n
m, most preferably 2.0 to 7.5 nm, Young's modulus of 130 to 160 is preferable, and 132 to 160 is more preferable.
The storage stability is preferably 7% or less, more preferably 5% or less, in the coercive force value, and preferably 7% or less, more preferably 5% or less in the saturation magnetization value.
It is as follows.

In the magnetic recording medium according to the present invention, a non-magnetic underlayer containing non-magnetic particle powder and a binder resin is formed between the non-magnetic support and the magnetic recording layer, if necessary. 4).

As the non-magnetic particle powder for the non-magnetic underlayer in the present invention, a non-magnetic inorganic powder generally used for the non-magnetic under layer for a magnetic recording medium can be used. Specifically, hematite, hydrous iron oxide, titanium oxide, zinc oxide, tin oxide, tungsten oxide, silicon dioxide, α-
Alumina, β-alumina, γ-alumina, chromium oxide,
Cerium oxide, silicon carbide, titanium carbide, silicon nitride, boron nitride, calcium carbonate, barium carbonate, magnesium carbonate, strontium carbonate, calcium sulfate, barium sulfate, molybdenum disulfide, barium titanate, etc. may be used alone or in combination. Yes, especially
Hematite, hydrous iron oxide, titanium oxide and the like are preferred.

In order to improve the dispersibility in the vehicle during the production of the non-magnetic paint, the surface of each of the non-magnetic particles was coated with aluminum hydroxide, aluminum oxide, silicon hydroxide and silicon hydroxide. The surface may be treated with an oxide or the like.Also, in order to improve various properties such as light transmittance, surface electric resistance, mechanical strength, surface smoothness, and durability of the obtained magnetic recording medium, Al is contained inside the particles. , Ti, Zr, Mn,
Sn, Sb, etc. may be contained.

Each non-magnetic particle powder includes particles of various shapes, such as spherical, granular, octahedral, hexahedral, polyhedral, etc., and acicular particles such as acicular, spindle-shaped, rice-granular, etc. Powder and plate-like particle powder. Considering the surface smoothness of the magnetic recording medium, a needle shape is preferable.

The particle size of each of the non-magnetic particle powders is, when the particle shape is granular, an average particle diameter of 0.01 to 0.3 μm.
Is preferably 0.02 to 0.2 μm, and when the particle shape is acicular, the average major axis diameter is 0.01 to 0.1 μm.
3 μm is preferable, and more preferably 0.02 to 0.2 μm
m, and when the particle shape is plate-like, the average plate surface diameter is 0.01
To 0.3 μm, more preferably 0.02 to
0.2 μm.

Further, when the particle shape is acicular, the axial ratio is 2 to 2.
20 is more preferable, and 3 to 10 is more preferable. When the particle shape is plate-like, the plate-like ratio (the ratio of the average plate surface diameter to the average thickness) (hereinafter, referred to as "plate-like ratio") is 2 to 50. Preferably, it is more preferably 3 to 10.

In the present invention, the coating thickness of the nonmagnetic underlayer is preferably in the range of 0.2 to 10.0 μm. If it is less than 0.2 μm, it becomes difficult to improve the surface roughness of the non-magnetic support. In consideration of the thinning of the magnetic recording medium and the surface smoothness of the coating film, more preferably 0.5 to 5.0 μm
Range.

The binder resin used in forming the magnetic recording layer can be used as the binder resin in the non-magnetic underlayer according to the present invention.

In the present invention, the mixing ratio of the nonmagnetic particle powder of the nonmagnetic underlayer and the binder resin is 100
The amount of the non-magnetic particle powder is preferably 5 to 2,000 parts by weight, more preferably 100 to 1000 parts by weight, based on parts by weight.

When the amount of the non-magnetic particles is less than 5 parts by weight, the amount of the non-magnetic particles in the non-magnetic paint is too small.
When a coating film is formed, a layer in which a nonmagnetic particle powder is continuously dispersed cannot be obtained, and the smoothness of the coating film surface becomes insufficient. 200
When the amount exceeds 0 parts by weight, the nonmagnetic particle powder is not sufficiently dispersed in the nonmagnetic paint because the amount of the nonmagnetic particle powder is too large relative to the amount of the binder resin, and as a result, a coating film is formed. In this case, it is difficult to obtain a coating film having a sufficiently smooth surface. Further, since the nonmagnetic particle powder is not sufficiently bound by the binder resin, the obtained coating film tends to be brittle.

The nonmagnetic underlayer contains a lubricant, an abrasive, an antistatic agent and the like generally used for a magnetic recording medium, if necessary, in an amount of about 0.1 to 50 parts by weight based on 100 parts by weight of the binder resin. It may be.

The nonmagnetic underlayer in the present invention preferably has a glossiness of the coating film of 176 to 300%, more preferably 18%.
0 to 300%, most preferably 184 to 300%, and the coating film surface roughness Ra is preferably 0.5 to 8.5 nm,
More preferably, it is 0.5 to 8.0 nm, and the strength of the coating film is preferably Young's modulus (relative value) of 124 to 160, more preferably 126 to 160.

The magnetic recording medium according to the fourth aspect of the present invention has a coercive force value of 63.7 to 278.5 kA / m (800 to 3500O
e) is preferred, more preferably 71.6 to 278.5.
kA / m (900 to 3500 Oe), squareness ratio (residual magnetic flux density Br / saturated magnetic flux density Bm) of 0.85 to 0.95, preferably 0.86 to 0.95, and the glossiness of the coating film It is preferably from 200 to 300%, more preferably from 205 to 300%, and the surface roughness Ra of the coating film is Ra 8.0.
nm or less, and more preferably 2.0 to 7.5 n
m, most preferably 2.0 to 7.0 nm, and a Young's modulus of 132 to 160 is preferable, and 134 to 160 is more preferable.
160, which is a change rate of the coercive force value of the storage stability of 7
% Or less, more preferably 5% or less, and the rate of change of the saturation magnetic flux density is preferably 7% or less, more preferably 5% or less.

[0079]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A typical embodiment of the present invention is as follows.

The average major axis diameter and average minor axis diameter of the particles were determined for the approximately 350 particles shown in the electron micrograph (× 30,000) enlarged four times in the vertical and horizontal directions, respectively. And the minor axis diameter were measured, and the average value was shown.

The axial ratio was shown by the ratio between the average major axis diameter and the average minor axis diameter.

The particle size distribution of the major axis of the particles was represented by a geometric standard deviation value obtained by the following method.

That is, the value obtained by measuring the major axis diameter of the particles shown in the enlarged photograph was calculated from the actual major axis diameter and the number of the particles calculated from the measured values, and the logarithmic normal On the probability paper, the horizontal axis represents the major axis diameter, and the vertical axis represents the percentage of the cumulative number of particles (under the integrated screen) belonging to each of the predetermined major axis diameter sections. Then, the value of the major axis diameter corresponding to 50% and 84.13% of the number of particles is read from this graph, and the geometric standard deviation value = the major axis diameter at 84.13% under the integrated screen / 50 under the integrated screen. %
The values calculated in accordance with the major axis diameter (geometric mean diameter) are shown. The closer the geometric standard deviation value is to 1, the better the particle size distribution of the major axis diameter of the particles.

The specific surface area was indicated by a value measured by the BET method.

The amount of Co and the amount of Al present inside the metal magnetic particle powder containing iron as a main component, the polyether modified polysiloxane coated on the composite metal magnetic particles containing a rare earth element and iron as a main component are contained. Each of the amounts of Si to be measured was measured using "X-ray fluorescence spectrometer 3063M" (manufactured by Rigaku Denki Kogyo Co., Ltd.) in accordance with JIS K0119 "General rules for X-ray fluorescence analysis".

For the soluble sodium salt in the metal magnetic particle powder containing iron as a main component and the composite metal magnetic particle powder containing iron as a main component, 5 g of a sample was weighed into a 300 ml Erlenmeyer flask, and 100 ml of boiling pure water was added. In addition, after heating and maintaining the boiling state for about 5 minutes, stopper and cool to room temperature, add water corresponding to the weight loss, stopper again and shake for 1 minute,
After standing for 5 minutes, the resulting supernatant was The solution was filtered using a 5C filter paper, and Na ⁺ in the filtrate was subjected to “inductively coupled plasma emission spectroscopy” (manufactured by Seiko Instruments Inc.).
It measured using.

The evaluation of the ease of loosening of the composite metal magnetic particles containing iron as a main component was carried out by crushing the composite metal magnetic particles containing iron as a main component with a finger or a roller, and by touching the powder at the time. A rating was given on a scale. 5: Squeezed immediately by just pressing with finger, no crush left. 4: It is crushed just by pressing with a finger, but a slight crush remains. 3: It is crushed just by pushing with a finger, but many crushes remain. 2: When crushed with a roller, it is crushed, but some grains remain. 1: When crushed with a roller, it is crushed, but many grains remain.

The magnetic properties of the metal magnetic particles containing iron as a main component and the composite metal magnetic particles containing iron as a main component are as follows.
Using a “vibrating sample magnetometer VSM-3S-15” (manufactured by Toei Industry Co., Ltd.), an external magnetic field of 795.8 kA / m (10
kOe), and the properties of the magnetic tape were measured under an external magnetic field of 795.8 kA / m (10 kOe).

The oxidation stability of the metal magnetic particles containing iron as a main component and the composite metal magnetic particles containing iron as a main component is as follows.
The sample powder was placed in an environment at a temperature of 60 ° C and a relative humidity of 90% for 15 minutes.
The sample was left for a few days, the coercive force values before and after the test were measured, and the value obtained by dividing the change by the value before the test was expressed as a percentage change rate.

The rate of change of the magnetic properties before and after the rinsing treatment was indicated by a value obtained by measuring the coercive force value and the saturation magnetization before and after the rinsing treatment, and dividing the change by the value before the rinsing.

The storage stability of the magnetic recording medium is determined by measuring the coercive force value and the saturation magnetization value before and after leaving the magnetic recording medium in an environment at a temperature of 60 ° C. and a relative humidity of 90% for 15 days. Was divided by the value before standing, and expressed as a percentage as a change rate.

The viscosity of the paint was measured at 25 ° C. using an “E-type viscometer EMD-R” (manufactured by Tokyo Keiki Co., Ltd.), and the shear rate D was 1.92 sec.
It was shown by the value at c ^{- 1} .

The surface gloss of the coating film was measured using a gloss meter “U
GV-5D "(manufactured by Suga Test Instruments Co., Ltd.) at an incident angle of 45 °, and the value when the standard plate gloss is 86.3% is shown in%.

The surface roughness Ra is expressed as “Surfcom-57
The center line average roughness of the coating film was measured using “5A” (manufactured by Tokyo Seimitsu Co., Ltd.).

The strength of the coating film was determined by measuring the Young's modulus of the coating film using “Autograph” (manufactured by Shimadzu Corporation). Young's Modulus is a commercially available videotape "AV T-12."
0 "(manufactured by Victor Company of Japan, Ltd.).
The higher the relative value, the better the strength of the coating film.

The thickness of each of the nonmagnetic support, the nonmagnetic underlayer, and the magnetic recording layer constituting the magnetic recording medium was measured by the following method.

Digital electronic micrometer K351C
First, the film thickness (A) of the nonmagnetic support is measured using (manufactured by Anritsu Electric Co., Ltd.). Next, the thickness (B) of the nonmagnetic support and the nonmagnetic underlayer formed on the nonmagnetic support
(Sum of the thickness of the nonmagnetic support and the thickness of the nonmagnetic underlayer)
Is measured in the same manner.

Next, the thickness (C) of the magnetic recording medium obtained by forming the magnetic recording layer on the nonmagnetic underlayer (the thickness of the nonmagnetic support, the thickness of the nonmagnetic underlayer, and the thickness of the magnetic recording layer) Is measured in the same manner. The thickness of the nonmagnetic underlayer is shown by (B)-(A), and the thickness of the magnetic recording layer is shown by (C)-(B).

The thickness of each layer of the magnetic recording medium having no nonmagnetic underlayer is determined by measuring the thickness (A) of the nonmagnetic support and the thickness (C) of the magnetic recording medium. Was determined as (C)-(A).

The surface tension of the aqueous solution was measured by using a Denui surface tension meter (manufactured by Nippon Oil Testing Machine Co., Ltd.), placing 15 ml of the measured aqueous solution in a 20 ml petri dish, immersing a thin platinum ring therein, and pulling up the platinum ring. The force at which the measured aqueous solution was separated from the liquid surface was measured, and the obtained value was obtained by inserting the obtained value into the following equation (1).

[0101]

## EQU1 ## Surface tension (mN / m) = T ₀ × (T ₂ / T ₁ ) T ₀ : 72.0 mN / m (surface tension of water at 25 ° C.) T ₁ : 68.2 ° (at 25 ° C.) (Measured value of water) T ₂ : Measured value of aqueous solution at 25 ° C.

<Production of composite metal magnetic particles containing iron as a main component> Needle-like metal magnetic particles containing iron as a main component and having been subjected to a surface oxidation treatment in advance (particle shape: spindle-shaped, average major axis diameter) 0.121 μm, average short axis diameter 0.0195 μm, axial ratio 6.2, geometric standard deviation value 1.42, BET specific surface area value 46.3 m ² / g, coercive force value 149.3 kA / m (1,
876 Oe) and a saturation magnetization value of 131.3 Am ² / kg (1
31.3 emu / g), the change rate of the coercive force value is 22.6%,
Change rate of saturation magnetization 19.4%, soluble sodium salt 2
65 ppm, Co content 2.10 wt%, Al content 0.70 wt%, Nd content 1.31 wt%) 10 kg
Was added to 100 l of pure water to obtain a slurry containing metal magnetic particle powder containing iron as a main component.

Using a filter thickener, the slurry containing the metal magnetic particles containing iron as a main component is concentrated and pure water is passed through, and the washing filtrate has an electric conductivity of 10 μS / c.
m or less.

Next, pure water is added to the slurry containing the metal magnetic particle powder containing iron as a main component to adjust the slurry concentration to 1%.
After adjusting to 00 g / l, 80 l of this slurry was added to a polyether-modified polysiloxane (trade name: BYK-080:
80g of Big Chemie Japan Co., Ltd.)
Stirring was performed for 15 minutes.

A slurry containing iron-based metal magnetic particle powder surface-treated with a polyether-modified polysiloxane was filtered, and then dried at 60 ° C. in a nitrogen stream using a dryer.
For 12 hours to obtain composite metal magnetic particle powder containing iron as a main component.

The obtained composite metal magnetic particles had a needle shape, an average major axis diameter of 0.121 μm, an average minor axis diameter of 0.0195 μm, and an axial ratio of 6.2. The geometric standard deviation value is 1.42, and the BET specific surface area value is 41.9 m ² /
g, the coercive force value is 145.0 kA / m (1,822 O
e), the saturation magnetization value is 128.4 Am ² / kg (128.
4 emu / g), 7 ppm of soluble sodium salt, change rate of coercive force value in oxidation stability of 7.1%, change rate of saturation magnetization value of 5.8%, ease of unraveling of 5, and Co content of 2 0.08 wt%, the Al content was 0.69 wt%, the Nd content was 1.28 wt%, and the coating amount of the polyether-modified polysiloxane was 0.24 wt% in terms of Si. The rate of change of the coercive force before and after the water washing treatment was 2.9%.
And the rate of change of the saturation magnetization was 2.2%.

Since the surface tension of an aqueous suspension containing iron-based metal magnetic particles cannot be directly measured, as a preliminary experiment, 80 mg of polyether-modified polysiloxane was added to 80 ml of pure water. When the surface tension of the solution was measured, it was 44.0 mN / m, which was lower than the surface tension of water (72.0 mN / m).

<Production of magnetic recording medium> 100.0 parts by weight of the obtained composite metal magnetic particles containing iron as a main component and a vinyl chloride-vinyl acetate copolymer resin (trade name: MR)
-110, manufactured by Zeon Corporation) 10.0 parts by weight, 23.3 parts by weight of cyclohexanone, methyl ethyl ketone 1
0.0 parts by weight, carbon black fine particle powder (manufactured by Mitsubishi Chemical Corporation, average particle diameter 26 nm, BET specific surface area 1
30 m ² / g) and 1.0 part by weight of alumina particles (AK
P-30, manufactured by Sumitomo Chemical Co., Ltd., average particle diameter 0.4 μ
m) After kneading 7.0 parts by weight with a kneader for 20 minutes, 79.6 parts by weight of toluene, 110.2 parts by weight of methyl ethyl ketone and 1 part by weight of cyclohexanone 1 were added to the kneaded product.
7.8 parts by weight were added for dilution, and then mixed and dispersed by a sand grinder for 3 hours to obtain a mixed dispersion.

To the above mixed dispersion, 33.3 parts by weight of a 1/1 solution of methyl ethyl ketone / toluene containing 10.0 parts by weight of a polyurethane resin solid content was added, and the mixture was further mixed and dispersed using a sand grinder for 30 minutes. Then, a 5/3/2 solution of methyl ethyl ketone / toluene / cyclohexanone containing 1.0 part by weight of myristic acid and 3.0 parts by weight of butyl stearate is added to the filtrate obtained by filtration through a filter having an opening of 1 μm. Methyl ethyl ketone / toluene / cyclohexanone 5/3/2 solution 1 containing 1 part by weight and 5.0 parts by weight of a trifunctional low molecular weight polyisocyanate (trade name: E-31, manufactured by Takeda Pharmaceutical Co., Ltd.) 1
5.2 parts by weight were mixed with stirring to obtain a magnetic paint.

The composition of the obtained magnetic paint was as follows. Composite metal magnetic particle powder containing iron as a main component 100.0 parts by weight, vinyl chloride-vinyl acetate copolymer resin 10.0 parts by weight, polyurethane resin 10.0 parts by weight, alumina particle powder 7.0 parts by weight, carbon black 1.0 part by weight of fine particle powder, 1.0 part by weight of myristic acid, 3.0 parts by weight of butyl stearate, 5.0 parts by weight of trifunctional low molecular weight polyisocyanate, 56.6 parts by weight of cyclohexanone, 141.5 parts by weight of methyl ethyl ketone Parts, 85.4 parts by weight of toluene.

The viscosity of the obtained magnetic paint was 8,159.
cP.

After the obtained magnetic coating material was filtered through a filter having a mesh size of 1 μm, it was applied on a polyethylene terephthalate film having a thickness of 12 μm using a slit coater having a gap width of 45 μm, and then dried to form a magnetic layer. After being formed and calendered by a conventional method to smooth the surface, it was cut into a width of 1.27 cm (１ ／ inch). The obtained magnetic tape was allowed to stand in a curing oven at 60 ° C. for 24 hours, and was sufficiently cured to obtain a magnetic tape. The thickness of the obtained coating film was 3.5 μm.

The magnetic properties of the magnetic tape obtained here were a coercive force value of 155.3 kA / m (1,951 Oe) and a squareness ratio (Br / Bm) of 0.89. Gloss 220
%, Surface roughness Ra was 6.1 nm, Young's modulus was 134, and among storage stability, the rate of change in coercive force was 3.6% and the rate of change in saturation magnetic flux density was 4.1%.

[0114]

The most important point in the present invention is that the metal magnetic particles containing iron as a main component are washed with water, and then the particles are subjected to a surface treatment with a polyether-modified polysiloxane to maintain good magnetic properties. This is a fact that a composite metal magnetic particle powder containing iron as a main component and having excellent oxidation stability, which has excellent dispersibility and reduced soluble salts as much as possible.

In the present invention, the metal magnetic particle powder containing iron as a main component, which has been stabilized by performing a surface oxidation treatment, is washed with water in the form of an aqueous suspension. The soluble sodium salt can be reduced more efficiently than in the case of washing with hematite particles in water.

Further, as described in the preliminary experiment described above, the surface tension of the solution can be reduced by adding the polyether-modified polysiloxane, so that the washing efficiency of the water-soluble salt is improved and the iron after the water washing is removed. The surface tension of the aqueous suspension containing the metal magnetic particles as the main component is reduced, the cohesion between the particles can be suppressed, and the composite metal magnetic particles containing iron as the main component that can be easily loosened can be obtained.
The surface tension can be reduced by an aqueous solution to which alcohol is added. However, when the surface tension is reduced to 45 mN / m or less by using alcohol, it is necessary to add 10% by weight or more. Because the solubility of the water-soluble salt is reduced in the solution in which the alcohol is added by the insolubility in the organic solvent and the interaction between the alcohol and water by the hydrogen bond, the washing efficiency tends to be further reduced. It is difficult to reduce the soluble salt, which is the object of the present invention. In the present invention, the desired effect of the present invention can be exhibited by adding a small amount of the polyether-modified polysiloxane, so that the water-soluble salt can be effectively reduced.

The reason why the composite metal magnetic particles containing iron as a main component and having excellent oxidation stability can be obtained is as follows.
The content of the soluble sodium salt in the composite metal magnetic particles containing iron as the main component can be reduced as much as possible, and the composite metal magnetic particles containing iron as the main component by subjecting the polyether-modified polysiloxane to a surface treatment It is believed that the oxidation of the compound could be suppressed.

Further, by using the composite metal magnetic particle powder containing iron as a main component having improved oxidation stability as the magnetic particle powder, the obtained magnetic recording medium also has excellent storage stability.

[0119]

Next, examples and comparative examples will be described.

Magnetic Particle Powders (a) to (c): As magnetic particle powders, metal magnetic particle powders containing iron as a main component and having the characteristics shown in Table 1 were prepared.

[0121]

[Table 1]

Examples 1 to 3 and Comparative Examples 1 and 2: Iron was mainly used in the same manner as in the embodiment of the present invention except that the type of magnetic particles, the presence or absence of the polyether-modified polysiloxane, and the amount of addition were varied. A composite metal magnetic particle powder as a component was obtained.

The production conditions at this time are shown in Table 2, and various characteristics of the obtained composite metal magnetic particles containing iron as a main component are shown in Table 3. The surface tension values in Table 2 are the surface tension values of a solution to which a polyether-modified polysiloxane was added so as to have a predetermined ratio with respect to 100 parts by weight of water.

[0124]

[Table 2]

[0125]

[Table 3]

<Manufacture of Magnetic Recording Medium> Examples 4 to 6, Comparative Examples 3 to 5: A magnetic recording medium was obtained in the same manner as in the embodiment of the present invention, except that the types of magnetic particles were variously changed. Was.

Table 4 shows the manufacturing conditions and various characteristics of the obtained magnetic recording medium.

[0128]

[Table 4]

<Production of Non-Magnetic Underlayer> Non-Magnetic Particles 1 to 6: Various properties of various non-magnetic particle powders used in Examples and Comparative Examples are shown in Table 5.

[0130]

[Table 5]

Underlayer 1: 12 g of hematite particles of nonmagnetic particles 1 shown in Table 6, a binder resin solution (30% by weight of a vinyl chloride-vinyl acetate copolymer resin having a sodium sulfonate group and 70% by weight of cyclohexanone), and A mixture (solid content: 72%) was obtained by mixing with cyclohexanone, and the mixture was further kneaded with a plastmill for 30 minutes to obtain a kneaded product.

This kneaded material was mixed with 1.5 mmφ glass beads 9
5 g, additional binder resin solution (30% by weight of polyurethane resin having sodium sulfonate group, 70% by weight of solvent (methyl ethyl ketone: toluene = 1: 1)), cyclohexanone, methyl ethyl ketone and toluene were added to a 140 ml glass bottle, and then added to a paint shaker. At 6
Mixing and dispersion were performed for a time to obtain a coating composition. Thereafter, a lubricant was added, and the mixture was further mixed and dispersed with a paint shaker for 15 minutes.

The composition of the obtained non-magnetic paint was as follows.

100 parts by weight of nonmagnetic particle powder, 10 parts by weight of a vinyl chloride-vinyl acetate copolymer resin having a sodium sulfonate group, 10 parts by weight of a polyurethane resin having a sodium sulfonate group, a lubricant (myristic acid: butyl stearate) = 1: 1) 2 parts by weight, 56.9 parts by weight of cyclohexanone, 142.3 parts by weight of methyl ethyl ketone, 85.4 parts by weight of toluene.

Next, the above non-magnetic paint was applied on a polyethylene terephthalate film having a thickness of 12 μm using a slit coater, and then dried to form a non-magnetic underlayer.

Table 6 shows the manufacturing conditions and various characteristics of the obtained nonmagnetic underlayer.

Underlayers 2 to 6: Nonmagnetic underlayers were obtained in the same manner as underlayer 1, except that the type of nonmagnetic particle powder was changed in various ways.

Table 6 shows the manufacturing conditions and various characteristics of the obtained nonmagnetic underlayer.

[0139]

[Table 6]

<Manufacture of Magnetic Recording Medium Having Non-Magnetic Underlayer> Example 7: A magnetic paint was obtained in the same manner as in the embodiment using the composite metal magnetic particle powder containing iron as a main component of Example 1. Was.

After applying a magnetic coating material on the base layer 1 to a thickness of 15 μm using a slit coater, orienting and drying in a magnetic field, and then slitting to a width of 1.27 cm (0.5 inch), After performing the calendar process, 60
A curing reaction was performed at 24 ° C. for 24 hours to obtain a magnetic tape.

Table 7 shows the manufacturing conditions and various characteristics of the obtained magnetic recording medium.

Examples 8 to 12 and Comparative Examples 6 to 8 Magnetic recording media were obtained in the same manner as in Example 7, except that the type of the nonmagnetic underlayer and the type of the magnetic particles were variously changed.

Table 7 shows the manufacturing conditions and various characteristics of the obtained magnetic recording medium.

[0145]

[Table 7]

[0146]

According to the present invention, iron having excellent oxidative stability due to having excellent dispersibility and reducing the soluble salt as much as possible while maintaining good magnetic properties can be obtained. Composite metal magnetic particle powder can be obtained.

The magnetic recording medium obtained by using the composite metal magnetic particles containing iron as a main component obtained by the present invention has a high coercive force value, a high saturation magnetization value and excellent dispersibility. It is suitable as a magnetic recording medium having high-density recording, high output, and improved storage stability.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4K018 BA13 BC29 BD02 5D006 BA04 BA07 EA01 FA01 FA09

Claims (4)

[Claims] 1. A polyether-modified polysiloxane having a mean major axis diameter of 0.02 to 0.30 μm and a sodium content of 10 ppm or less is coated on each particle surface of iron-based metal magnetic particle powder. S for metal magnetic particles
A composite metal magnetic particle powder containing iron as a main component, which is attached in an amount of 0.02 to 10% by weight in terms of i. 2. An aqueous suspension containing the iron-based metal magnetic particles after dispersing the iron-based metal magnetic particles in an aqueous solution and washing with an aqueous suspension. The solution is added with 0.02 to 10 parts by weight of a polyether-modified polysiloxane in terms of Si based on the amount of metal magnetic particles containing iron as a main component in the aqueous suspension, stirred, dehydrated and filtered. The method for producing a composite metal magnetic particle powder containing iron as a main component according to claim 1. 3. A magnetic recording medium comprising a non-magnetic support and a magnetic recording layer comprising a magnetic resin powder and a binder resin formed on the non-magnetic support, wherein the magnetic particle powder is the iron according to claim 1. A magnetic recording medium characterized by being a composite metal magnetic particle powder containing as a main component. 4. A non-magnetic support, a non-magnetic underlayer comprising a non-magnetic particle powder formed on the non-magnetic support and a binder resin, and a magnetic particle powder formed on the non-magnetic under layer A magnetic recording medium comprising a magnetic recording layer containing a dispersing agent resin, wherein the magnetic particle powder is the composite metal magnetic particle powder containing iron as a main component according to claim 1.